1. Field of the Invention
This invention relates to a wafer processing method, and more particularly to a wafer processing method for manufacturing wafers which have material-contaminant-gettering damage formed on one surface.
2. Description of the Related Art
Wafers used for the manufacture of semiconductor devices are formed as follows: First, a silicon monocrystalline ingot is sliced into wafers. Thereafter, both surfaces of each wafer are subjected to lapping and etching processes and damage is formed only on the back side surface (which is the side opposite to the main surface in which semiconductor elements are formed in the later steps) by means of honing. After this, the wafer is cleaned and the main surface, in which semiconductor elements are formed, is polished to a mirror finish.
The reason for using honing to form damage is as follows: As the semiconductor device is formed with higher integration density and is more miniaturized, requirements for a high quality become stronger. It is well known in the art that a wafer is formed to have gettering capability by forming damage on the back side surface thereof in order to attain a wafer of high quality. A honing method is known as a method for forming the back side damage (BSD) or damage on the back side surface of the wafer. The honing method is effected by spraying fine particles such as SiO.sub.2 onto the back side surface of the wafer to form damage thereon. However, with this method, damages of as large as several .mu.m may to be formed, and if a wafer with such large damages is subjected to a device manufacturing process such as an oxidation process, silicon dust will be produced from the damages and attached as fine particles to the main surface of the wafer. Due to that contamination, a significant effect occurs in the fine pattern processing, lowering the manufacturing yield.
With the wafer having no BSD formed on the back side surface, the above problem does not occur. However, in this case, the wafer has no gettering capability and therefore the main surface of the wafer is easily influenced by accidental process fluctuation or contamination. For example, in the oxidation step, an oxidation induced stacking fault (OSF) may occur in the surface. As a result, leakage current flowing across the pn junction increases or image defect will occur in an image sensor, thus lowering the manufacturing yield.
As described above, in the conventional wafer processing method of forming wafers having damages formed on the back side surface thereof, the damage site size becomes too large, degrading the process to be effected later.